If you mean it's like floating above the ground, the only way to fix it really is to open the aircraft.cfg file, find the contact points section (this would be easier to do in FSEdit) and change the "height" of the landing gear to be lower. complicated, yes. but it's the only solution. So let's say the gear is at -10.2. Try adjusting it by one or two feet at a time unless your Concorde is SERIOUSLY off lol.